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AC unit turns on blower doesn't come on

Central air unit with furnace function working fine, but switched to ''cool'' fan is set to ''auto''. Outside AC unit turns on fine but blower never kicks on inside the furnace. I've had trouble with the limit switch in the past, but replaced it and everything worked fine. I tried fiddling with the unit and if the limit switch leads are hardwired (basically eliminating a faulty limit switch) no blower and no error indicator light, but disconnecting them kicks on the blower (infinitely) but, also gives an open limit error on the board. I don't imagine the limit plays into the AC function? but it's the only thing I know I've had trouble with. Not sure what actually triggers the blower to start on AC what to check?
The Furnace is a Janitrol GPD100-4 REV-B

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  • word2thewhys
    word2thewhys Jun 19, 2009

    The thermostat is working correctly, it's activating the AC unit outside it also works for the heater.

  • word2thewhys
    word2thewhys Jun 19, 2009

    I wanted to make sure I understand, There isn't a fan relay problem but probably another relay? I should check the RC terminal for any type of current? At what point should I be looking for a current? when the AC is on or when the blower should be turning on? Also this terminal is likely located somewhere on the board will it be labeled? Also can you tell me the consequences of each...if I have current that means...? If I do not have a current that means...?

  • word2thewhys
    word2thewhys Jun 19, 2009

    Non-digital thermostat - Honeywell. I just realized you were talking about the the thermostat I think... and not inside the furnace? I just want to reiterate, The thermostat kicks on the AC unit outside so you still think it may be a thermostat issue? Or am I confused and we are talking about terminals on the board in the furnace?



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The thermostat is the controller.

Posted on Jun 19, 2009

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  • Ned C Cook
    Ned C Cook Jun 19, 2009

    Signal from thermostat is not being made to the fan relay. You should hear a click at the furnce when you lower the temp. .You don't appear to have a fan relay problem. The fan limit awitch default is closed so when the relay is tripped it interupts the limit switch circuit to the fan. Make sense? So it's a smaller relay that causes interupt with the low voltage from the thermostat.. If you can, ck the RC terminal tfor current. That is the red cool term.

  • Ned C Cook
    Ned C Cook Jun 19, 2009

    If you have current the blower should kick on. If there is no current , then it won't. the terminals are marked. The red and rc should be jumped I should have asked. Is this a digital thermostat or round? and what brans is it?

  • Ned C Cook
    Ned C Cook Jun 20, 2009

    The thermostat



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